USB (Universal Serial Bus) and IEEE-1394 (IEEE Standard for a High Performance Serial Bus) are widely used as standards to interface various devices, for example, PCs, printers, scanners, DVD drives, digital video cameras, etc. In recent years, USB and IEEE-1394 have been attracting attention as interfaces for data transferring on cellular telephones, mobile music players, etc.
USB 2.0 interfaces have a maximum transfer speed of 480 Mbps. IEEE-1394 interfaces have a maximum transfer speed of 400 Mbps. Because the data transfer speeds of USB interfaces and IEEE-1394 interfaces are high, data is sent or received by using low voltage differential signals (small amplitude differential signals). A current-driven differential driver is used to send the data.
In an example current-driven differential driver, a current source included in the current-driven differential driver requires time to stabilize the performance thereof when the current-driven differential driver switches from a no-output state to an output state. In a known method for constantly stabilizing the current source, the current-driven differential driver passes a current therein as a throwaway current even at the no-output state when data is transferred at high speed.
However, power saving is required in cellular telephones, mobile music players, etc. Therefore, a method for saving such a throwaway current has been proposed. One type of current-driven differential driver includes a current source, a throwaway current path, and a switching device provided in the throwaway current path. The switching device prevents the throwaway current from flowing when no data is transferred. In this method, the switching device is turned on before each time data is transferred. The switching device is turned on at the timing to allow an adequate time for the current source to be stabilized. Therefore, waiting time is required for each time data is transferred.